Production of high quality diesel by supercritical water process

ABSTRACT

A method for producing a diesel having improved cold flow properties, the method comprising the steps of introducing a crude oil to a distillation column, separating the crude oil in the distillation unit to produce a light gas oil, and a light vacuum gas oil, where the light gas oil has a T95% cut point in the range between 300 deg C. and 340 deg C., where the light vacuum gas oil has a T95% cut point in the range between 400 deg C. and 430 deg C., processing the light vacuum gas oil in the supercritical water unit to produce an upgraded vacuum gas oil, separating the upgraded vacuum gas oil in the fractionator to produce an upgraded light fraction, an upgraded light gas oil, and upgraded heavy fraction, introducing the upgraded light gas oil into a diesel pool, and blending the light gas oil into the diesel pool.

TECHNICAL FIELD

Disclosed are methods for producing diesel. Specifically, disclosed aremethods and systems for producing diesel with enhanced cold flowproperties.

BACKGROUND

Wax components in diesel start to solidify and form crystals attemperatures below the cloud point temperature. The cloud pointtemperature can depend on the location, season, and grade of dieselfuel, ranging from 10 degrees Celsius (deg C.) and −33 deg C. Thesolidified wax components, typically in the saturates or paraffinfraction of diesel, can result in a cloudy appearance in the diesel. Thesolid fraction crystals can plug fuel supply line and engine parts, suchas fuel filters. Cold flow properties of diesel, which can relate to thewax formation, are characterized by cloud point (CP), pour point (PP),and cold filter plugging point (CFPP). In arctic climate zones, thecloud point of diesel must be lower than −10 degrees Celsius (deg C.)according to the European Committee for Standardization, EN 590.

One current method to improve cold flow properties is blending inlighter fractions such as naphtha and kerosene. Blending can impact theproperties of diesel. Blending of large quantities of light fractionscan negatively affect density, lubricity, flash point, and Cetane indexof diesel. In addition, blending can perturb product distribution in arefinery.

Another method includes adding additives such as cloud point depressant.The downsides of adding additives include increasing the cost of thediesel and adding complexity to the production process.

A third method is undercutting of diesel. Paraffins in the high boilingrange are responsible for poor cold flow properties. Paraffins can beremoved by reducing the distillation cut point of diesel, butdistillation results in loss of diesel to the vacuum gas oil andatmospheric residue fraction, both of which have a lower value ascompared to diesel.

A fourth method is solvent dewaxing. In a solvent dewaxing process,aliphatic ketone solvents, such as methyl ethyl ketone (MEK) or methylisobutyl ketone (MIBK), are used to crystallize wax components at lowtemperatures and then can separate from non-waxy component. A solventdewaxing process can result in low liquid yield and difficulty inrecovering solvents and is not often used in distillate dewaxing.Solvent dewaxing can remove high boiling range paraffins, however thismethod reduces liquid yield.

A fifth method is catalytic dewaxing. In catalytic dewaxing, long chainparaffins are cracked or isomerized selectively to decrease the cloudpoint and cold filter plugging point. In a typical catalytic dewaxing, azeolite-based catalyst is used. The drawbacks of catalytic dewaxing arethe loss of diesel to kerosene or naphtha by cracking. In addition,catalytic dewaxing is not suitable for non-hydrotreated feedstockbecause nitrogen and sulfur compounds are inhibitors to dewaxingcatalysts.

Finally, it is noted that aromatics can improve cold flow properties,but EN590 provides limits on the amount of aromatics that can be presentin diesel. Straight run diesel, the “as-distilled” fraction from crudeoil typically contains low amounts of aromatics. Blending light cycleoil (LCO) fraction from an FCC unit can increase the aromatic content,but only to a limited extent.

SUMMARY

Disclosed are methods for producing diesel. Specifically, disclosed aremethods and systems for producing diesel with enhanced cold flowproperties.

In a first aspect, a method for producing a diesel having improved coldflow properties is provided. The method includes the steps ofintroducing a crude oil to a distillation column, separating the crudeoil in the distillation unit to produce a light gas oil, and a lightvacuum gas oil, where the light gas oil has a T95% cut point in therange between 300 deg C. and 340 deg C., where the light vacuum gas oilhas a T95% cut point in the range between 400 deg C. and 430 deg C.,introducing the light vacuum gas oil to a supercritical upgrading unit,processing the light vacuum gas oil in the supercritical water unit toproduce an upgraded vacuum gas oil, introducing the upgraded vacuum gasoil to a fractionator, separating the upgraded vacuum gas oil in thefractionator to produce an upgraded light fraction, an upgraded lightgas oil, and upgraded heavy fraction, introducing the upgraded light gasoil into a diesel pool, where the diesel pool includes diesel, andblending the light gas oil into the diesel pool.

In certain aspects, the diesel in the diesel pool meets the standards ofEN590. In certain aspects, the diesel in the diesel pool has a cloudpoint of less than −3 deg C., further where the diesel has a CFPP ofless than −20 deg C., and further where the diesel has a pour point ofless than −18 deg C. In certain aspects, the method further includes thesteps of separating a light fraction stream in the distillation column,where the light fraction stream has a T95% cut point of less than 240deg C., mixing the upgraded light fraction with the light fractionstream to produce a mixed light stream, and introducing the mixed lightstream to a naphtha and kerosene pool. In certain aspects, the methodfurther includes the steps of separating a heavy vacuum gas oil in thedistillation column, where the heavy vacuum gas oil has a T95% cut pointof between 560 deg C., separating a vacuum residue stream in thedistillation column, where the vacuum residue stream has a T5% cut pointof greater than 560 deg C., mixing the heavy vacuum gas oil and thevacuum residue stream to produce a mixed heavy stream, and introducingthe mixed heavy stream to a reside upgrading unit. In certain aspects,the resid upgrading unit is selected from the group consisting of fluidcatalytic cracking (FCC) unit, resid FCC, hydrocracker, residhydrodesulfurization (RHDS) hydrotreater, visbreaker, coker, gasifier,and solvent extractor. In certain aspects, the method further includesthe steps of separating a residue slip stream from vacuum residuestream, mixing the residue slip stream with the light vacuum gas oil toproduce mixed vacuum gas oil stream, and introducing mixed vacuum gasoil to the supercritical upgrading unit. In certain aspects, the step ofprocessing the light vacuum gas oil in the supercritical water unitincludes the step of increasing the pressure of the light vacuum gas oilin a hydrocarbon pump to produce a pressurized hydrocarbon feed, wherethe pressure of the pressurized hydrocarbon feed is greater than thecritical pressure of water, increasing the temperature of pressurizedhydrocarbon feed in a hydrocarbon heater to produce a hot hydrocarbonstream, where the temperature of the hot hydrocarbon stream is between10 deg C. and 300 deg C., mixing the hot hydrocarbon stream with asupercritical water in a mixer to produce a mixed feed stream,introducing the mixed feed stream to a supercritical reactor, where thetemperature in the supercritical reactor is in the range between 380 degC. and 600 deg C. and the pressure in the supercritical reactor is inthe range between 3203 psig and 5150 psig, where the residence time inthe supercritical reactor is in the range between 10 seconds and 60minutes, allowing conversion reactions in the supercritical reactor toproduce an effluent stream such that the mixed feed stream undergoesconversion reactions, reducing the temperature of the effluent stream toa cooling device to produce a cooled stream, where the cooled stream isat a temperature in the range between 10 deg C. and 200 deg C., reducingthe pressure of the cooled stream in a depressurizing device to producea modified stream, where the pressure of modified stream is in the rangebetween 0 psig and 300 psig, introducing the depressurizing device to aseparator, separating the modified stream in the separator to produce agases stream and a liquid stream, introducing the liquid stream to anoil-water separator, and separating the liquid stream in the oil-waterseparator to produce the upgraded vacuum gas oil and a water product. Incertain aspects, the distillation column is in the absence of anexternal supply of catalyst, further where the supercritical upgradingunit is in the absence of an external supply of catalyst, and furtherwhere the fractionator is in the absence of an external supply ofcatalyst. In certain aspects, the distillation column is in the absenceof an external supply of hydrogen, further where the supercriticalupgrading unit is in the absence of an external supply of hydrogen, andfurther where the fractionator is in the absence of an external supplyof hydrogen.

In a second aspect, a method for producing a diesel having improved coldflow properties is provided. The method includes the steps ofintroducing a crude oil to a distillation column, separating the crudeoil in the distillation unit to produce a light gas oil, and a lightvacuum gas oil, where the light gas oil has a T95% cut point in therange between 300 deg C. and 340 deg C., where the light vacuum gas oilhas a T95% cut point in the range between 400 deg C. and 430 deg C.,introducing the light gas oil to a gas oil hydrodesulfurization unit,where the gas oil hydrodesulfurization unit operates at a temperature inthe range between 300 deg C. and 420 deg C., where the gas oilhydrodesulfurization unit operates at a pressure between 100 psig and1050 psig, where the gas oil hydrodesulfurization unit operates at aliquid hourly space velocity between 0.5 h−1 and 6 h−1, where the gasoil hydrodesulfurization unit includes a hydrodesulfurization catalyst,processing the light gas oil in the gas oil hydrodesulfurization unit toproduce a desulfurized light gas oil, introducing the light vacuum gasoil to a supercritical upgrading unit, processing the light vacuum gasoil in the supercritical water unit to produce an upgraded vacuum gasoil, introducing the upgraded vacuum gas oil to an upgradinghydrodesulfurization unit, where the upgrading hydrodesulfurization unitoperates at a temperature in the range between 300 deg C. and 420 degC., where the upgrading hydrodesulfurization unit operates at a pressurebetween 100 psig and 1050 psig, where the upgrading hydrodesulfurizationunit operates at a liquid hourly space velocity between 0.5 h−1 and 6h−1, where the upgrading hydrodesulfurization unit includes ahydrodesulfurization catalyst, processing the upgraded vacuum gas oil inthe hydrodesulfurization unit to produce a desulfurized vacuum gas oil,introducing the desulfurized vacuum gas oil to a fractionator,separating the desulfurized vacuum gas oil in the fractionator toproduce an upgraded light fraction, an upgraded light gas oil, and anupgraded heavy fraction, introducing the upgraded light gas oil into adiesel pool, where the diesel pool includes diesel, and blending thedesulfurized light gas oil into the diesel pool.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the scope willbecome better understood with regard to the following descriptions,claims, and accompanying drawings. It is to be noted, however, that thedrawings illustrate only several embodiments and are therefore not to beconsidered limiting of the scope as it can admit to other equallyeffective embodiments.

FIG. 1 provides a process diagram of an embodiment of the process.

FIG. 2 provides a process diagram of an embodiment of the supercriticalupgrading unit.

FIG. 3 provides a process diagram of an embodiment of the process.

FIG. 4 provides a pictorial representation of the components indifferent boiling point ranges.

FIG. 5 provides a process diagram of an embodiment of the process.

FIG. 6 provides a process diagram of an embodiment of the process.

In the accompanying Figures, similar components or features, or both,may have a similar reference label.

DETAILED DESCRIPTION

While the scope of the apparatus and method will be described withseveral embodiments, it is understood that one of ordinary skill in therelevant art will appreciate that many examples, variations andalterations to the apparatus and methods described here are within thescope and spirit of the embodiments.

Accordingly, the embodiments described are set forth without any loss ofgenerality, and without imposing limitations, on the embodiments. Thoseof skill in the art understand that the scope includes all possiblecombinations and uses of particular features described in thespecification.

Described here are processes and systems for a diesel upgrading processwith improved cold flow properties as compared to a conventional dieselupgrading process. Advantageously, the diesel upgrading process canimprove the cold flow properties without using hydrogen and catalyst,while increasing the production yield of diesel by at least between 2%and 5% as compared to conventional processes. Advantageously, the dieselupgrading process can improve refining margins. Advantageously, thediesel upgrading process has improved cold flow properties withoutsacrificing liquid yield. Advantageously, the diesel upgrading processcan produce an increase of short chain aromatics in the light dieselfraction, useful as feedstock for benzene, toluene, xylene (BTX)production.

As used throughout, “external supply of hydrogen” refers to the additionof hydrogen to the feed to the reactor or to the reactor itself. Forexample, a reactor in the absence of an external supply of hydrogenmeans that the feed to the reactor and the reactor are in the absence ofadded hydrogen, gas (H₂) or liquid, such that no hydrogen (in the formH₂) is a feed or a part of a feed to the reactor.

As used throughout, “external supply of catalyst” refers to the additionof catalyst to the feed to the reactor or the presence of a catalyst inthe reactor, such as a fixed bed catalyst in the reactor. For example, areactor in the absence of an external supply of catalyst means nocatalyst has been added to the feed to the reactor and the reactor doesnot contain a catalyst bed in the reactor.

As used throughout, “cold flow properties” refers to one or more of thefollowing properties of diesel: cloud point (CP), pour point (PP), andcold filter plugging point (CFPP).

As used throughout, “cloud point” refers to the temperature below whichwax in diesel forms a cloudy appearance. Cloud point can be measuredaccording to ASTM D5772 and ASTM D2500.

As used throughout, “pour point” refers to the lowest temperature atwhich a liquid remains pourable, a high pour point is typically relatedto a high paraffin content. Pour point can be measured according to ASTMD5950.

As used throughout, “cold filter plugging point” or “CFPP” refers to thelowest temperature at which a given volume of diesel will still flowthrough a specific, standardized filter. Cold filter plugging pointaccording to ASTM D6371.

As used throughout, “diesel” refers to a composite of hydrocarbonshaving a boiling point range between an initial boiling point of 130 degC. and a final boiling point of 390 deg C. Both initial boiling pointand final boiling point can be measured by ASTM D86.

As used throughout, “T95% cut point” refers to distillation recoverytemperature at which 95 percent (%) of the hydrocarbons in a streamevaporate.

As used throughout, “EN 590” refers to CEN/TC 19—Gaseous and liquidfuels, lubricants and related products of petroleum, synthetic andbiological origin, at reference number EN 950:2013+A13:2017, whichdescribes the properties required for automotive diesel fuel for use indiesel engines. EN 590 specifies that the T95% cut point of diesel isless than 360 deg C.

As used throughout, “atmospheric residue” or “atmospheric residuefraction” refers to the fraction of oil-containing streams having aninitial boiling point (IBP) of 650 deg F, such that all of thehydrocarbons have boiling points greater than 650 deg F and includes thevacuum residue fraction. Atmospheric residue can refer to thecomposition of an entire stream, such as when the feedstock is from anatmospheric distillation unit, or can refer to a fraction of a stream,such as when a whole range crude is used.

As used throughout, “vacuum residue” or “vacuum residue fraction” refersto the fraction of oil-containing streams having an IBP of 1050 deg F.Vacuum residue can refer to the composition of an entire stream, such aswhen the feedstock is from a vacuum distillation unit or can refer to afraction of stream, such as when a whole range crude is used.

As used throughout, “asphaltene” refers to the fraction of anoil-containing stream which is not soluble in a n-alkane, particularly,n-heptane.

As used throughout, “heavy fraction” refers to the fraction in thepetroleum feed having a true boiling point (TBP) 10% that is equal to orgreater than 650 deg F (343 deg C.), and alternately equal to or greaterthan 1050 deg F (566 deg C.). Examples of a heavy fraction can includethe atmospheric residue fraction or vacuum residue fraction. The heavyfraction can include components from the petroleum feed that were notconverted in the supercritical water reactor. The heavy fraction canalso include hydrocarbons that were dimerized or oligomerized in thesupercritical water reactor due to either lack of hydrogenation orresistance to thermal cracking.

As used throughout, “distillable fraction” or “distillate” refers to thehydrocarbon fraction lighter than the distillation residue from anatmospheric distillation process or a vacuum distillation process.

As used throughout, “coke” refers to the toluene insoluble materialpresent in petroleum.

As used throughout, “cracking” refers to the breaking of hydrocarbonsinto smaller ones containing few carbon atoms due to the breaking ofcarbon-carbon bonds.

As used throughout, “upgrade” means one or all of increasing APIgravity, decreasing the amount of impurities, such as sulfur, nitrogen,and metals, decreasing the amount of asphaltene, and increasing theamount of distillate in a process outlet stream relative to the processfeed stream. One of skill in the art understands that upgrade can have arelative meaning such that a stream can be upgraded in comparison toanother stream, but can still contain undesirable components such asimpurities.

As used here, “conversion reactions” refers to reactions that canupgrade a hydrocarbon stream including cracking, isomerization,alkylation, dimerization, aromatization, cyclization, desulfurization,denitrogenation, deasphalting, and demetallization.

As used here, “Cetane number” or “Cetane Number” refers to the ignitioncharacteristics of diesel fuel and can be measured according to ASTM613. The Cetane Number can be estimated from actual engine testing.

As used here, “Cetane index” refers to the calculated value from thedensity and distillation range to characterize ignition properties ofdiesel fuel. The Cetane index does not incorporate data from actualengine testing. The Cetane index can be measured according to ASTM D4737and ASTM D976.

As used here, “gas-to-liquid (GTL) processes” refers to processes toconvert natural gas to liquid fuel through catalytic conversion. GTLprocesses can produce highly paraffinic liquid fuel.

The following embodiments, provided with reference to the figures,describe the upgrading process.

Referring to FIG. 1, a process flow diagram of a diesel upgradingprocess is provided. Crude oil 10 is introduced to distillation column100. Crude oil 10 can be any source of crude oil including crude oilderived from gas-to-liquid (GTL) processes. In at least one embodiment,crude oil 10 is not derived from biomass materials.

Distillation column 100 can be any type of separation unit capable ofseparating a hydrocarbon stream into component parts. An example ofdistillation column 100 includes an atmospheric distillation column.Distillation column 100 can be operated to separate naphtha, kerosene,light gas oil, light vacuum gas oil, and heavy vacuum gas oil.Distillation column 100 can operate based on targeted cut points ofdistillation.

Distillation column 100 can produce light fraction stream 20, light gasoil 30, light vacuum gas oil 40, heavy vacuum gas oil 50, and vacuumresidue stream 60. In an alternate embodiment, distillation column 100can produce a light fraction stream, a light gas oil, a light vacuum gasoil, and a heavy stream, where the heavy stream contains the heavyvacuum gas oil and the vacuum residue stream. Light fraction stream 20can have a T95% cut point of less than 240 deg C. Light fraction stream20 can contain naphtha and kerosene. Light fraction stream 20 can beintroduced to naphtha and kerosene pool 500.

Light gas oil 30 can have a T95% cut point in the range between 300 degC. and 340 deg C. Light gas oil 30 can contain light gas oil. Light gasoil 30 can be introduced to diesel pool 600. The diesel upgradingprocess undercuts the light gas oil fraction as compared to aconventional separation unit which conventional separation unit producesa light gas oil stream having a T95% cut point in the range between 340deg C. and 380 deg C.

Light vacuum gas oil 40 can have a T95% cut point in the range between400 deg C. and 430 deg C. Light vacuum gas oil 40 can contain lightvacuum gas oil. The diesel upgrading process wide cuts the light vacuumgas oil fraction as compared to a conventional separation unit whichproduces a light vacuum gas oil stream having a T95% cut point in therange between 400 deg C. and 430 deg C. Light vacuum gas oil 40 can beintroduced to supercritical upgrading unit 200.

Heavy vacuum gas oil 50 can have a T95% cut point of greater than 560deg C. Heavy vacuum gas oil 50 can contain heavy vacuum gas oil. Heavyvacuum gas oil 50 is not introduced or processed in supercriticalupgrading unit 200.

Vacuum residue stream 60 can have a T5% cut point of greater than 560deg C. Vacuum residue stream 60 can include vacuum residue fraction.Vacuum residue stream 60 contains the heaviest fraction of crude oil. Inat least one embodiment, vacuum residue stream 60 is not controlled bydistillation but is the remainder fraction not separated in heavy vacuumgas oil 50.

Heavy vacuum gas oil 50 and vacuum residue stream 60 can be mixed toproduce mixed heavy stream 55. Mixed heavy stream 55 can be introducedto resid upgrading unit 400. Resid upgrading unit 400 can be any processunit capable of upgrading a heavy fraction stream. Examples of residupgrading unit 400 include fluid catalytic cracking (FCC) unit, residFCC, hydrocracker, resid hydrodesulfurization (RHDS) hydrotreater,visbreaker, coker, gasifier, and solvent extractor. Resid upgrading unit400 can produce resid upgraded product 90.

Supercritical upgrading unit 200 can process light vacuum gas oil 40 toproduce upgraded vacuum gas oil 70. Supercritical upgrading unit 200 canbe described with reference to FIG. 2.

Water feed 202 is introduced to supercritical upgrading unit 200. Waterfeed 202 can be a demineralized water having a conductivity less than1.0 microSiemens per centimeter (μS/cm), alternately less 0.5 μS/cm, andalternately less than 0.1 μS/cm. In at least one embodiment, water feed20 is demineralized water having a conductivity less than 0.1 μS/cm.Water feed 20 can have a sodium content less than 5 micrograms per liter(μg/L) and alternately less than 1 μg/L. Water feed 20 can have achloride content less than 5 μg/L and alternately less than 1 μg/L.Water feed 20 can have a silica content less than 3 μg/L.

Water feed 202 can be passed to water pump 204. Water pump 204 can beany type of pump capable of increasing the pressure of water feed 202.In at least one embodiment, water pump 204 is a diaphragm metering pump.The pressure of water feed 202 can be increased in water pump 204 toproduce pressurized water 205. The pressure of pressurized water 205 canbe greater than the critical pressure of water. Pressurized water 205can be introduced to water heater 208.

Water heater 208 can be any type of heat exchanger capable of increasingthe temperature of pressurized water 205. Examples of heat exchangersthat can be used as water heater 208 can include an electric heater, afired heater, a cross exchanger, and other known heaters. Thetemperature of pressurized water 205 can be increased in water heater208 to produce supercritical water 210. The temperature of supercriticalwater 210 can be equal to or greater than the critical temperature ofwater, alternately between 374 deg C. and 600 deg C., and alternatelybetween 400 deg C. and 550 deg C.

Light vacuum gas oil 40 can be passed to hydrocarbon pump 214.Hydrocarbon pump 214 can be any type of pump capable of increasing thepressure of light vacuum gas oil 40. In at least one embodiment,hydrocarbon pump 214 is a diaphragm metering pump. The pressure of lightvacuum gas oil 40 can be increased in hydrocarbon pump 214 to a pressuregreater than the critical pressure of water to produce pressurizedhydrocarbon feed 215. Pressurized hydrocarbon feed 215 can be passed tohydrocarbon heater 218.

Hydrocarbon heater 218 can be any type of heat exchanger capableincreasing the temperature of pressurized hydrocarbon feed 215. Examplesof heat exchangers capable of being used as hydrocarbon heater 218 caninclude an electric heater, a fired heater, a cross exchanger, and otherknown heaters. In at least one embodiment, hydrocarbon heater 218 can becross exchanged with effluent stream 245. The temperature of pressurizedhydrocarbon feed 215 can be increased in hydrocarbon heater 218 toproduce hot hydrocarbon stream 225. The temperature of hot hydrocarbonstream 225 can be between 10 deg C. and 300 deg C. and alternatelybetween 50 deg C. and 200 deg C. Maintaining the temperature of hothydrocarbon stream 225 at less than 300 deg C. reduces the formation ofcoke in hot hydrocarbon stream 225 and in supercritical reactor 240.

Hot hydrocarbon stream 225 and supercritical water 210 can be passed tomixer 230. Mixer 230 can be any type of mixing device capable of mixinga petroleum stream and a supercritical water stream. Examples of mixingdevices suitable for use as mixer 230 can include a static mixer, aninline mixer, an impeller-embedded mixer, and other known mixers. Theratio of the volumetric flow rate of light vacuum gas oil 40 to waterfeed 202 can be in the range between 1:1 and 1:10 at standardtemperature and pressure (SATP), alternately between 1:1 and 1:5 atSATP, alternately between 1:1 and 1:2, alternately greater than 1:1.05,and alternately greater than 1:1.1. In at least one embodiment, thevolumetric flow rate of water feed 202 is greater than the volumetricflow rate of light vacuum gas oil 40 to minimize and alternately preventthe recombination of cracked molecules by dilution. Advantageously,having a volumetric flow rate of water feed 202 that is greater than thevolumetric flow rate of light vacuum gas oil 40 can minimize thermalcracking reactions that can occur without the presence of supercriticalwater, thus can minimizing the formation of coke and gas. Hothydrocarbon stream 225 and supercritical water 210 can be mixed toproduce mixed feed 44. The pressure of mixed feed stream 235 can begreater than the critical pressure of water. The temperature of mixedfeed stream 235 can depend on the temperatures of supercritical water210 and hot hydrocarbon stream 225. Mixed feed stream 235 can beintroduced to supercritical reactor 240.

Supercritical reactor 240 can include one or more reactors in series.Supercritical reactor 240 can be any type of reactor capable of allowingconversion reactions. Examples of reactors suitable for use insupercritical reactor 240 can include tubular-type, vessel-type,CSTR-type, and combinations of the same. In at least one embodiment,supercritical reactor 240 includes a tubular reactor, whichadvantageously prevents precipitation of reactants or products.Supercritical reactor 240 can include an upflow reactor, a downflowreactor, and a combination of an upflow reactor and downflow reactor. Inat least one embodiment, supercritical reactor 240 includes an upflowreactor, which advantageously prevents channeling of reactants resultingin an increased reaction yield. Advantageously, by processing only thelight vacuum gas oil in supercritical reactor 240, the size ofsupercritical reactor 240 can be reduced relative to a supercriticalwater reactor that processes the entire crude oil portion. Supercriticalreactor 240 is in the absence of an external supply of catalyst. In atleast one embodiment, supercritical reactor 240 is in the absence of anexternal supply of hydrogen.

The temperature in supercritical reactor 240 can be maintained atgreater than the critical temperature of water, alternately in the rangebetween 380 deg C. and 600 deg C., and alternately in the range between390 deg C. and 450 deg C. The pressure in supercritical reactor 240 canbe maintained at a pressure in the range between 3203 pounds per squareinch gauge (psig) and 5150 psig and alternately in the range between3300 psig and 4300 psig. The residence time of the reactants insupercritical reactor 240 can between 10 seconds and 60 minutes andalternately between 5 minute and 30 minutes. The residence time iscalculated by assuming that the density of the reactants insupercritical reactor 240 is the same as the density of water at theoperating conditions of supercritical reactor 240.

The reactants in supercritical reactor 240 can undergo conversionreactions to produce effluent stream 245. Effluent stream 245 can beintroduced to cooling device 250.

Cooling device 250 can be any type of heat exchange device capable ofreducing the temperature of effluent stream 245. Examples of coolingdevice 250 can include double pipe type exchanger and shell-and-tubetype exchanger. In at least one embodiment, cooling device 250 can be across exchanger with pressurized hydrocarbon feed 215. The temperatureof effluent stream 245 can be reduced in cooling device 250 to producecooled stream 255. The temperature of cooled stream 255 can be between10 deg C. and 200 deg C. and alternately between 30 deg C. and 150 degC. Cooled stream 255 can be introduced to depressurizing device 260.

Depressurizing device 260 can be any type of device capable of reducingthe pressure of a fluid stream. Examples of depressurizing device 260can include a pressure let-down valve, a pressure control valve, and aback pressure regulator. The pressure of cooled stream 255 can bereduced to produce modified stream 265. Modified stream 265 can bebetween 0 psig and 300 psig.

Modified stream 265 can be introduced to separator 270. Separator 270can be any type of separation device capable of separating a fluidstream into gas phase and liquid phase. Modified stream 265 can beseparated to produce gases stream 272 and liquid stream 275. Liquidstream 275 can be introduced to oil-water separator 280.

Oil-water separator 280 can be any type of separation device capable ofseparating a fluid stream into a hydrocarbon containing stream and awater stream. Liquid stream 275 can be separated in oil-water separator280 to produce upgraded vacuum gas oil 70 and water product 285.

Water product 285 can be treated and recycled to front of thesupercritical upgrading unit or can be disposed.

Upgraded vacuum gas oil 70 can contain less than 200 parts-per-millionby weight (ppm wt) water. The conditions in oil-water separator 280 canbe adjusted to attain upgraded vacuum gas oil 70 with an amount of waterless than 200 ppm wt. In at least one embodiment, upgraded vacuum gasoil 70 can be subjected to a dehydration process to reduce the amount ofwater following the oil-water separator if needed to reduce the amountof water to 200 ppm wt or less. The dehydration process can include anadsorption bed.

Upgraded vacuum gas oil 70 can contain naphtha range components,kerosene range components, and light gas oil range components.Supercritical upgrading unit 200 is in the absence of a step or processto recycle upgraded vacuum gas oil 70, such that upgraded vacuum gas oilis not recycled in supercritical upgrading unit 200. Upgraded vacuum gasoil 70 can have a reduced cloud point as compared to light vacuum gasoil 40.

Treating light vacuum gas oil 40 in supercritical upgrading unit 200 canproduce upgraded vacuum gas oil 70 having hydrocarbons in the naphtharange, kerosene range, and light gas oil range. Advantageously, treatinglight vacuum gas oil 40 in supercritical upgrading unit 200 can cracklong chain paraffins, normal paraffins and aromatics with alkylsubstitutes in light vacuum gas oil 40. Upgraded vacuum gas oil 70 canhave shorter chain paraffins than are present in light vacuum gas oil40. Long chain paraffins, such as paraffins with at least 24 carbonatoms, can have a greater melting point than shorter chain paraffins.Long chain paraffins with at least 24 carbon atoms have a boiling ofabout 340 deg C., which is in the range of diesel fuel with a T95% cutpoint of between 330 deg C. and 360 deg C. Upgraded vacuum gas oil 70can have light gas oil range alkylaromatics, which have a lower meltingpoint than paraffins. In at least one embodiment, light gas oil rangealkylaromatics do not include toluene, which is in the naphtha rangealkylaromatics. Advantageously, aromatization can occur in supercriticalupgrading unit 200. It is understood that olefins, formed from thermalcracking of paraffins, can be cyclized and dehydrogenated into aromaticsduring a supercritical water process. By generating aromatics, thesupercritical upgrading process improves the cold flow properties of theupgraded vacuum gas oil, as compared to a hydrocracker or hydrotreater,which decreases the aromatic content in the product stream.

Advantageously, treating light vacuum gas oil in supercritical upgradingunit 200 eliminates or minimizes the production of coke, such thatsolids separation in supercritical upgrading unit 200 is not required.

Returning to FIG. 1, upgraded vacuum gas oil 70 can be introduced tofractionator 300.

Fractionator 300 can be any type of separation unit capable ofseparating a stream containing hydrocarbons. Examples of fractionator300 can include a distillation column having multiple-stages of internalreflux and a flashing column. Fractionator 300 can produce upgradedlight fraction 75, upgraded light gas oil 80, and upgraded heavyfraction 85.

Upgraded light fraction 75 can contain the naphtha range hydrocarbonsand kerosene range hydrocarbons present in vacuum gas oil 70. Upgradedlight fraction 75 can be mixed with light fraction stream 20 to producemixed light stream 25 and introduced to naphtha and kerosene pool 500.In at least one embodiment, upgraded light fraction 75 can be introducedto naphtha and kerosene pool 500 without first mixing with lightfraction stream 20.

Upgraded light gas oil 80 can contain the light gas oil rangehydrocarbons present in vacuum gas oil 70. The conditions infractionator 300 can be adjusted such that the T95% cut point ofupgraded light gas oil 80 meets the EN 590 specification. In at leastone embodiment, the light gas oil in upgraded light gas oil 80 hasimproved cold flow properties as compared to the light gas oil in lightgas oil 30. Fractionator 300 can include one or more separation units.The separation units can include an atmospheric distillation column, avacuum distillation column, and combinations of the same. Theatmospheric distillation column can produce naphtha, kerosene, gas oil,atmospheric residue, and combinations of the same. The atmosphericdistillation column can operate at a temperature between 250 deg C. and350 deg C. and a pressure between 0.5 atmospheres (atm) and 1.5 atm. Thevacuum distillation column can separate the atmospheric residue toproduce light vacuum gas oil, heavy vacuum gas oil, vacuum residue, andcombinations of the same. The vacuum distillation column can operate ata temperature between 250 deg C. and 430 deg C. and a pressure between10 millimeters of mercury (mmHg) absolute (10-100 Torr). In at least oneembodiment, fractionator 300 can include an atmospheric distillationcolumn and a vacuum distillation column.

Upgraded light gas oil 80 can be mixed into diesel pool 600. Diesel pool600 can contain diesel. The separation conditions that produce light gasoil 30 and upgraded light gas oil 80 can be adjusted to produce a dieselpool containing diesel that meets the standards of EN 590. Diesel indiesel pool 600 can have a density between 0.820 kilograms per liter(kg/l) and 0.845 kg/l measured at 15 deg C., a Cetane number of greaterthan 51, a Cetane index of greater than 46, a flash point of greaterthan 55 deg C., a total sulfur content of less than 10 parts-per-millionby weight (wt ppm) sulfur, T95% cut point of less than 360 deg C., apolycyclic aromatics content of less than 11 wt %, a cloud point of lessthan −10 deg C. (corresponding to the arctic region, class 0), a pourpoint of −22 deg C., and a CFPP of less than −20 deg C. (correspondingto arctic region, class 0). Advantageously, the overall yield of dieselin the present process is greater than conventional diesel formingprocess. The diesel in diesel pool can be hydrotreated to reduce thesulfur content to below 10 wt ppm.

Upgraded heavy fraction 85 can contain the hydrocarbons heavier than thehydrocarbons in upgraded light gas oil 80, including unconvertedfractions from supercritical upgrading unit 200.

Heavy vacuum gas oil 50 is not introduced to supercritical upgradingunit 200 because while supercritical water can crack alkyl substituteson polycyclic aromatics it cannot open the aromatic rings. Heavy vacuumgas oil tends to have greater quantities of polycylic aromatics ascompared to light vacuum gas oil. Thus, submitting heavy vacuum gas oilto supercritical upgrading unit 200 would produce a light gas oilproduct with increased amounts of polycyclic aromatics. Due to thelimits on polycyclic aromatics in diesel, the heavy vacuum gas oil isnot treated in supercritical upgrading unit 200.

An alternate embodiment for the diesel upgrading process is describedwith reference to FIG. 3 and FIG. 1. Light gas oil 30 is introduced togas oil hydrodesulfurization unit 700 to produce desulfurized light gasoil 35. Gas oil hydrodesulfurization unit 700 removes sulfur from lightgas oil 30.

Gas oil hydrodesulfurization unit 700 can operate at a temperature inthe range between 300 deg C. and 420 deg C. and alternately between 320deg C. and 380 deg C. The pressure can be in the range between 100 psigand 1050 psig, alternately between 150 psig and 750 psig. The liquidhourly space velocity (LHSV) can be between 0.5 per hour (h⁻¹) and 6 h⁻¹and alternately between 1 h⁻¹ and 4 h⁻¹. Gas oil hydrodesulfurizationunit 700 can include a hydrodesulfurization catalyst. Thehydrodesulfurization catalyst can include cobalt molybdenum sulfideswith aluminum oxide (CoMoS/Al₂O₃), nickel molybdenum sulfides withaluminum oxide (NiMoS/Al₂O₃), and combinations of the same. Thehydrodesulfurization catalyst can include promoters such as boron,phosphorous, and zeolites. Hydrogen gas can be added to the gas oilhydrodesulfurization unit 700. The ratio of the volumetric flow rate ofthe hydrogen gas to light gas oil 30 can be in the range from 30 normalcubic meters per cubic meters (Nm³/m³) and 300 Nm³/m³, and alternatelyin the range from 100 Nm³/m³ and 250 Nm³/m³.

Advantageously, the light gas oil in light gas oil 30 can be in theabsence of refractory sulfur compounds, such as 4,6-DMDBT, and alkylcarbazoles, such as 1, 8-dimethylcarbazole, which are both stronginhibitors for a hydrodesulfurization catalyst. The absence ofrefractory sulfur compounds and alkyl carbazoles is due to the T95% cutpoint of light gas oil 30, as can be seen in FIG. 4 As a result of theabsence of refactory sulfur compounds and alkyl carbazoles, light gasoil 30 will have a high activity in a hydrodesulfurization unit.Consequently, gas oil hydrodesulfurization unit 700 can operate undermild conditions, such as pressures less than 1050 psig and LHSV greaterthan 0.5 h⁻¹, which increases liquid yield. Operating at thehydrodesulfurization unit at mild conditions can minimize the loss ofdiesel hydrocarbon molecules due to such molecules being hydrocrackedinto naphtha range hydrocarbons and kerosene range hydrocarbons. At thesame time, hydrodesulfurization can achieve deep desulfurization oflight gas oil 30.

Desulfurized light gas oil 35 can contain less than 10 ppm wt sulfur.Desulfurized light gas oil 35 can be introduced to diesel pool 600.

Upgraded vacuum gas oil 70 can be processed in upgradinghydrodesulfurization unit 750 to produce desulfurized vacuum gas oil 95.

Upgrading hydrodesulfurization unit 750 can be at a temperature in therange between 320 deg C. and 420 deg C. and alternately between 340 degC. and 400 deg C. The pressure can be in the range between 450 psig and1500 psig, alternately between 400 psig and 1050 psig. The liquid hourlyspace velocity (LHSV) can be between 0.25 per hour (h⁻¹) and 4 h⁻¹ andalternately between 1 h⁻¹ and 3 h⁻¹. Upgrading hydrodesulfurization unit750 can include the hydrodesulfurization catalyst. Thehydrodesulfurization catalyst can include cobalt molybdenum withaluminum oxide (CoMoS/Al₂O₃), nickel molybdenum with aluminum oxide(NiMoS/Al₂O₃), and combinations of the same. The hydrodesulfurizationcatalyst can include promoters such as boron, phosphorous, and zeolites.Hydrogen gas can be added to the upgrading hydrodesulfurization unit750. The ratio of the volumetric flow rate of the hydrogen gas toupgraded vacuum gas oil 70 can be in the range from 100 Nm³/m³ and 600Nm³/m³, and alternately in the range from 150 Nm³/m³ and 400 Nm³/m³.

Advantageously, subjecting light vacuum gas oil 40 to supercriticalupgrading unit 200 results in upgrading a portion of the light vacuumgas oil to smaller molecules, which results in enhancedhydrodesulfurization activity. Supercritical upgrading unit 200 reducesthe amount of heavier sulfur compounds and the amount of aromatics.Consequently, upgrading hydrodesulfurization unit 750 can operate undermild conditions, such as pressures less than 1500 psig and LHSV greaterthan 0.25 h⁻¹, which increases liquid yield. Operating at thehydrodesulfurization unit at mild conditions can minimize the loss ofdiesel hydrocarbon molecules due to such molecules being hydrocrackedinto naphtha range hydrocarbons and kerosene range hydrocarbons.

Desulfurized vacuum gas oil 95 can contain less than 300 ppm wt.Desulfurized vacuum gas oil 95 can be introduced to fractionator 300.Upgraded light gas oil 80 can contain less than 10 ppm wt sulfur. Theremaining sulfur is present in upgraded heavy fraction 85.

An alternate embodiment for the diesel upgrading process is describedwith reference to FIG. 5 and FIG. 1.

Residue slip stream 65 can be separated from vacuum residue stream 60.Residue slip stream 65 can contain the vacuum residue fraction. Any unitcapable of separating a slip stream can be used. In at least oneembodiment, residue slip stream 65 is separated through a three wayvalve. Residue slip stream 65 can be mixed with light vacuum gas oil 40to produce mixed vacuum gas oil stream 45. The flow rate of residue slipstream 65 can be adjusted such that the amount of the vacuum residuefraction present in mixed vacuum gas oil stream 45 can be between 0.1 wt% and 10 wt % and alternately between 1 wt % and 5 wt %. Advantageously,vacuum residue fraction has aliphatic sulfur compounds that can generatehydrogen sulfide during reaction. Hydrogen sulfide is a known hydrogentransfer agent. In addition, vacuum residue contains other naturalhydrogen donors which can be utilized with the aid of hydrogen sulfide.Therefore, by adding an amount of the vacuum residue fraction to thelight vacuum gas oil in light vacuum gas oil 40 the conversion rate insupercritical upgrading unit 200 can be increased while a reduced amountof olefins in the diesel range are produced. In addition, processing apart of the vacuum residue fraction in supercritical upgrading unit 200can reduce the load to resid upgrading unit 400.

Mixed vacuum gas oil stream 45 can be introduced to supercriticalupgrading unit 200. Supercritical upgrading unit 200 can be operated asdescribed with reference to FIG. 2, where the pressure of mixed vacuumgas oil stream 45 can be increased in hydrocarbon pump.

In at least one embodiment, the diesel upgrading process is in theabsence of an external supply of hydrogen. In at least one embodiment,the diesel upgrading process is in the absence of an external supply ofcatalyst.

EXAMPLES Example 1

The Example was conducted by a lab scale unit. Example 1 is acomparative example where crude oil was separated in an atmosphericdistillation column to produce a light gas oil. The crude oil was anArabian Light Crude oil having an API gravity of 35 degrees and a totalsulfur content of 1.7 wt %. The volumetric flow rate of the crude oilwas 400,000 barrels per day (bpd). The atmospheric distillation columnwas operated such that the T95% of the light gas oil was 357 deg C.,producing a flow rate of the light gas oil of 100,000 barrels per day.The light gas oil was a straight-run light gas oil. The cloud point ofthe light gas oil was −5 deg C. The target cloud point value was −10 degC., thus the cloud point of the light gas oil in Example 1 was greaterthan the target cloud point. The properties of the light gas oil can befound in Table 1.

Example 2

The Example was conducted by a lab scale unit, according to the processdescribed with reference to FIG. 6. Crude oil 10 was separated indistillation column 100 to produce light gas oil 30. Crude oil 10 was anArabian Light Crude oil having an API gravity of 35 degrees and a totalsulfur content of 1.7 wt %. The volumetric flow rate of crude oil 10 was400,000 barrels per day (bpd). Distillation column 100 produced lightgas oil 30 and light vacuum gas oil 40. Light gas oil 30 was producedwith a narrow cut point having a final boiling point between 300 deg C.and 340 deg C., while light vacuum gas oil 40 was produced with a widercut having a final boiling point 400 deg C. and 430 deg C. Light vacuumgas oil 40 was introduced to supercritical upgrading unit 200 to producesupercritical product oil 70.

Supercritical upgrading unit 200, described with reference FIG. 2, wasoperated as follows. The ratio of the volumetric flow rate of water feed202 to light vacuum gas oil 40 was 2:1 as measured at standardatmospheric temperature and pressure. The pressure of both pressurizedwater 205 and pressurized hydrocarbon feed 215 was 3,600 psig. Thetemperature of supercritical water 210 was 450 deg C. The temperature ofhot hydrocarbon stream 225 was 150 deg C. Mixer 230 was a simple teefitting. Supercritical reactor 240 was operated at 450 deg C. and aresidence time of 3.5 minutes. Effluent stream 245 was cooled in coolingdevice 250 to a temperature of 90 deg C., where cooling device 250 was ashell and tube type cross exchanger that heated water feed 202 and asecond shell and tube exchanger. Cooled stream 255 was depressurized indepressurizing device 260 to atmospheric pressure. Modified stream 265was separated in separator 270 to produce gases stream 272 and liquidstream 275. Liquid stream 275 was separated in oil-water separator 280to produce supercritical product oil 70 and water product 280.

Supercritical product oil 70 and light gas oil 30 are both introduced tofractionator 300. Fractionator 300 produced upgraded light gas oil 80,upgraded light fraction 75, and upgraded heavy fraction 85. Theproperties of certain streams are in Table 1.

TABLE 1 Properties of various streams. Example 1 Example 2 Example 2Example 2 Example 2 Light gas Light gas Light Vacuum SupercriticalUpgraded Light Stream Properties oil oil 10 Gas Oil 40 Product Oil 70Gas Oil 80 Volume Flow (barrel/day) 100,824 79,852 64,986 65,667 123,580API (deg) 37.1 39.5 28.2 34.4 39.5 TBP 5% 210 201 316 273 212 TBP 10%221 212 326 287 223 TBP 30% 252 238 35 318 258 TBP 50% 281 261 372 344287 TBP 70% 312 284 395 370 312 TBP 90% 345 311 421 408 347 TBP 95% 357321 431 416 358 Sulfur Content (wt %) 1.06 0.82 1.97 1.29 0.79 CetaneIndex, ASTM D4737 54.5 53.8 — — 55.1 Cloud Point (deg C.) −5 −14 — — −12

Upgraded light gas oil 80 had a cloud point of −12 deg C., while theT95% was about 360 deg C. The flow rate of upgraded light gas oil 80 wasgreater than the flow rate of the light gas oil from Example 1.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

There various elements described can be used in combination with allother elements described here unless otherwise indicated.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed here as from about one particular value to aboutanother particular value and are inclusive unless otherwise indicated.When such a range is expressed, it is to be understood that anotherembodiment is from the one particular value to the other particularvalue, along with all combinations within said range.

Throughout this application, where patents or publications arereferenced, the disclosures of these references in their entireties areintended to be incorporated by reference into this application, in orderto more fully describe the state of the art to which the inventionpertains, except when these references contradict the statements madehere.

As used here and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

That which is claimed is:
 1. A method for producing a diesel havingimproved cold flow properties, the method comprising the steps of:introducing a crude oil to a distillation column; separating the crudeoil in the distillation unit to produce a light gas oil, and a lightvacuum gas oil, where the light gas oil has a T95% cut point in therange between 300 deg C. and 340 deg C., where the light vacuum gas oilhas a T95% cut point in the range between 400 deg C. and 430 deg C.;introducing the light vacuum gas oil to a supercritical upgrading unit;processing the light vacuum gas oil in the supercritical water unit toproduce an upgraded vacuum gas oil; introducing the upgraded vacuum gasoil to a fractionator; separating the upgraded vacuum gas oil in thefractionator to produce an upgraded light fraction, an upgraded lightgas oil, and upgraded heavy fraction; introducing the upgraded light gasoil into a diesel pool, where the diesel pool comprises diesel; andblending the light gas oil into the diesel pool.
 2. The method of claim1, where the diesel in the diesel pool meets the standards of EN590. 3.The method of claim 1, where the diesel in the diesel pool has a cloudpoint of less than −3 deg C., further where the diesel has a CFPP ofless than −20 deg C., and further where the diesel has a pour point ofless than −18 deg C.
 4. The method of claim 1, further comprising thesteps of: separating a light fraction stream in the distillation column,where the light fraction stream has a T95% cut point of less than 240deg C.; mixing the upgraded light fraction with the light fractionstream to produce a mixed light stream; and introducing the mixed lightstream to a naphtha and kerosene pool.
 5. The method of claim 1, furthercomprising the steps of: separating a heavy vacuum gas oil in thedistillation column, where the heavy vacuum gas oil has a T95% cut pointof between 560 deg C.; separating a vacuum residue stream in thedistillation column, where the vacuum residue stream has a T5% cut pointof greater than 560 deg C.; mixing the heavy vacuum gas oil and thevacuum residue stream to produce a mixed heavy stream; and introducingthe mixed heavy stream to a reside upgrading unit.
 6. The method ofclaim 5, where the resid upgrading unit is selected from the groupconsisting of fluid catalytic cracking (FCC) unit, resid FCC,hydrocracker, resid hydrodesulfurization (RHDS) hydrotreater,visbreaker, coker, gasifier, and solvent extractor.
 7. The method ofclaim 5, further comprising the steps of: separating a residue slipstream from vacuum residue stream; mixing the residue slip stream withthe light vacuum gas oil to produce mixed vacuum gas oil stream; andintroducing mixed vacuum gas oil to the supercritical upgrading unit. 8.The method of claim 1, where the step of processing the light vacuum gasoil in the supercritical water unit comprises the steps of: increasingthe pressure of the light vacuum gas oil in a hydrocarbon pump toproduce a pressurized hydrocarbon feed, where the pressure of thepressurized hydrocarbon feed is greater than the critical pressure ofwater; increasing the temperature of pressurized hydrocarbon feed in ahydrocarbon heater to produce a hot hydrocarbon stream, where thetemperature of the hot hydrocarbon stream is between 10 deg C. and 300deg C.; mixing the hot hydrocarbon stream with a supercritical water ina mixer to produce a mixed feed stream; introducing the mixed feedstream to a supercritical reactor, where the temperature in thesupercritical reactor is in the range between 380 deg C. and 600 deg C.and the pressure in the supercritical reactor is in the range between3203 psig and 5150 psig, where the residence time in the supercriticalreactor is in the range between 10 seconds and 60 minutes; allowingconversion reactions in the supercritical reactor to produce an effluentstream such that the mixed feed stream undergoes conversion reactions;reducing the temperature of the effluent stream to a cooling device toproduce a cooled stream, where the cooled stream is at a temperature inthe range between 10 deg C. and 200 deg C; reducing the pressure of thecooled stream in a depressurizing device to produce a modified stream,where the pressure of modified stream is in the range between 0 psig and300 psig; introducing the depressurizing device to a separator;separating the modified stream in the separator to produce a gasesstream and a liquid stream; introducing the liquid stream to anoil-water separator; and separating the liquid stream in the oil-waterseparator to produce the upgraded vacuum gas oil and a water product. 9.The method of claim 1, where the distillation column is in the absenceof an external supply of catalyst, further where the supercriticalupgrading unit is in the absence of an external supply of catalyst, andfurther where the fractionator is in the absence of an external supplyof catalyst.
 10. The method of claim 1, where the distillation column isin the absence of an external supply of hydrogen, further where thesupercritical upgrading unit is in the absence of an external supply ofhydrogen, and further where the fractionator is in the absence of anexternal supply of hydrogen.
 11. A method for producing a diesel havingimproved cold flow properties, the method comprising the steps of:introducing a crude oil to a distillation column; separating the crudeoil in the distillation unit to produce a light gas oil, and a lightvacuum gas oil, where the light gas oil has a T95% cut point in therange between 300 deg C. and 340 deg C., where the light vacuum gas oilhas a T95% cut point in the range between 400 deg C. and 430 deg C.;introducing the light gas oil to a gas oil hydrodesulfurization unit,where the gas oil hydrodesulfurization unit operates at a temperature inthe range between 300 deg C. and 420 deg C., where the gas oilhydrodesulfurization unit operates at a pressure between 100 psig and1050 psig, where the gas oil hydrodesulfurization unit operates at aliquid hourly space velocity between 0.5 h⁻¹ and 6 h⁻¹, where the gasoil hydrodesulfurization unit comprises a hydrodesulfurization catalyst;processing the light gas oil in the gas oil hydrodesulfurization unit toproduce a desulfurized light gas oil; introducing the light vacuum gasoil to a supercritical upgrading unit; processing the light vacuum gasoil in the supercritical water unit to produce an upgraded vacuum gasoil; introducing the upgraded vacuum gas oil to an upgradinghydrodesulfurization unit, where the upgrading hydrodesulfurization unitoperates at a temperature in the range between 300 deg C. and 420 degC., where the upgrading hydrodesulfurization unit operates at a pressurebetween 100 psig and 1050 psig, where the upgrading hydrodesulfurizationunit operates at a liquid hourly space velocity between 0.5 h⁻¹ and 6h⁻¹, where the upgrading hydrodesulfurization unit comprises ahydrodesulfurization catalyst; processing the upgraded vacuum gas oil inthe hydrodesulfurization unit to produce a desulfurized vacuum gas oil;introducing the desulfurized vacuum gas oil to a fractionator;separating the desulfurized vacuum gas oil in the fractionator toproduce an upgraded light fraction, an upgraded light gas oil, andupgraded heavy fraction; introducing the upgraded light gas oil into adiesel pool, where the diesel pool comprises diesel; and blending thedesulfurized light gas oil into the diesel pool.
 12. The method of claim11, where the diesel in the diesel pool meets the standards of EN590.13. The method of claim 11, where the diesel in the diesel pool has acloud point of less than −3 deg C., further where the diesel has a CFPPof less than −20 deg C., and further where the diesel has a pour pointof less than −18 deg C.
 14. The method of claim 11, further comprisingthe steps of: separating a light fraction stream in the distillationcolumn, where the light fraction stream has a T95% cut point of lessthan 240 deg C.; mixing the upgraded light fraction with the lightfraction stream to produce a mixed light stream; and introducing themixed light stream to a naphtha and kerosene pool.
 15. The method ofclaim 11, further comprising the steps of: separating a heavy vacuum gasoil in the distillation column, where the heavy vacuum gas oil has aT95% cut point of between 560 deg C.; separating a vacuum residue streamin the distillation column, where the vacuum residue stream has a T5%cut point of greater than 560 deg C.; mixing the heavy vacuum gas oiland the vacuum residue stream to produce a mixed heavy stream; andintroducing the mixed heavy stream to a reside upgrading unit.
 16. Themethod of claim 15, where the resid upgrading unit is selected from thegroup consisting of fluid catalytic cracking (FCC) unit, resid FCC,hydrocracker, resid hydrodesulfurization (RHDS) hydrotreater,visbreaker, coker, gasifier, and solvent extractor.
 17. The method ofclaim 15, further comprising the steps of: separating a residue slipstream from vacuum residue stream; mixing the residue slip stream withthe light vacuum gas oil to produce mixed vacuum gas oil stream; andintroducing mixed vacuum gas oil to the supercritical upgrading unit.18. The method of claim 11, where the step of processing the lightvacuum gas oil in the supercritical water unit comprises the steps of:increasing the pressure of the desulfurized light vacuum gas oil in ahydrocarbon pump to produce a pressurized hydrocarbon feed, where thepressure of the pressurized hydrocarbon feed is greater than thecritical pressure of water; increasing the temperature of pressurizedhydrocarbon feed in a hydrocarbon heater to produce a hot hydrocarbonstream, where the temperature of the hot hydrocarbon stream is between10 deg C. and 300 deg C.; mixing the hot hydrocarbon stream with asupercritical water in a mixer to produce a mixed feed stream;introducing the mixed feed stream to a supercritical reactor, where thetemperature in the supercritical reactor is in the range between 380 degC. and 600 deg C. and the pressure in the supercritical reactor is inthe range between 3203 psig and 5150 psig, where the residence time inthe supercritical reactor is in the range between 10 seconds and 60minutes; allowing conversion reactions in the supercritical reactor toproduce an effluent stream such that the mixed feed stream undergoesconversion reactions; reducing the temperature of the effluent stream toa cooling device to produce a cooled stream, where the cooled stream isat a temperature in the range between 10 deg C. and 200 deg C.; reducingthe pressure of the cooled stream in a depressurizing device to producea modified stream, where the pressure of modified stream is in the rangebetween 0 psig and 300 psig; introducing the depressurizing device to aseparator; separating the modified stream in the separator to produce agases stream and a liquid stream; introducing the liquid stream to anoil-water separator; and separating the liquid stream in the oil-waterseparator to produce the upgraded vacuum gas oil and a water product.19. The method of claim 11, where the distillation column is in theabsence of an external supply of catalyst, further where thesupercritical upgrading unit is in the absence of an external supply ofcatalyst, and further where the fractionator is in the absence of anexternal supply of catalyst.
 20. The method of claim 11, where thedistillation column is in the absence of an external supply of hydrogen,further where the supercritical upgrading unit is in the absence of anexternal supply of hydrogen, and further where the fractionator is inthe absence of an external supply of hydrogen.